The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon.
Having begun using anti-radiation homing missiles (ARM) 30 years ago during the Vietnam War to suppress hostile air defense radars, the U.S. military has used ARM""s in every conflict since then. In an ARM, a microwave receiver on the missile is tuned to the frequency of the threat radar to enable it to acquire the radar. Upon acquisition, the received frequency is processed to derive direction finding (DF) information which is subsequently provided to the missile""s autopilot. The result is a more direct hit of the missile on the target radar.
While its operation sounds fairly straightforward, ARM""s suffer from two major problems. One is that if no target radar turns on during the discover-and-destroy mission, the ARM is totally useless. Another is that ARM""s typically are not able to hit the target radars when some of the radar""s energy bounces off the ground around the radar and gives a false target. Further, air defense radars usually blink (i.e. turn on and off) as a countermeasure, resulting in a low kill probability for the threat radar.
Thus it is desirable to have a dual or multi-mode seeker weapon that has both an active mode, such as millimeter wave (MMW) or Imaging Infrared (IIR), and a passive mode radio-frequency (RF) homing capability. Such a multi-mode seeker has two main advantages. The first is that if no emitting air defense radar is encountered, the weapon can still be used in the active mode since the active mode requires no emission from the target. The MMW radar on the missile emits signals that are reflected from the target and received back at the missile by MMW antenna 201. The second is that the active mode can also be used for the terminal portion of the missile""s flight, after the missile has flown the initial and mid-course portions using the passive mode, to decrease any miss distance from the target radar.
The drawbacks to dual/multi-mode weapons are their cost and the present inability to put physically all of the required hardware into the missile due to limited space.
Applicants"" Passive Radar Detector for Dualizing Missile Seeker Capability overcomes the drawbacks mentioned above by incorporating a passive RF detector into a standard active MMW seeker missile with a minimum of microwave hardware modifications. To accomplish this, anti-radiation homing (ARH) antennas and down conversion elements are added to the missile. The added antennas intercept the air defense radar emission signals and the conversion elements convert the intercepted signals to the intermediate frequency (IF) usable by the MMW radar. The IF can then be processed by the signal processor that already exists as a part of the MMW seeker. Using the existing processor greatly reduces both the size and cost of having a passive supplemental detector for detecting hostile radars.